Class 'SimpleXMLElement' not found on puphpet PHP 5.6

I faced this issued and finally solved by run following command :

apt install php5.6-xml

After it reload and restart apache2 service :

service apache2 reload   

service apache2 restart

And a PHP restart may be required

systemctl restart php-fpm

The problem was that I was using Cent OS and in this Linux Distribution, the php-libxml package does not come as default.

I ended up generating a new machine through PuPHPet GUI and added to the System Package the following packages to be installed:

php-xml, php-simplexml

Problem solved.

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For those using PHP 7 and Ubuntu, @MPS solved it by running apt-get install php7.0-xml and service apache2 restart.

On Centos, we need to install the XML php package. You can try yum install php56w-xml or yum install php70w-xml if you're using php70w repository for PHP 7.0